1. Field of the Invention
The present invention relates to a touch panel, and more particularly, to a structure of a touch panel formed over a liquid crystal display panel.
2. Discussion of the Related Art
In order to more efficiently use various electronic machines, touch panels have generally been used to input signals on display surfaces, thereby eliminating additional remote controllers or other input devices. Touch panels are widely integrated with display surfaces of flat display devices such as electronic calculators, liquid crystal display (LCD) devices, plasma display panel (PDP) devices, electroluminescence (EL) devices, and cathode ray tubes (CRTs). By integrating touch panels with display devices, it is possible for a user to select desired information while watching an image displayed by the display device.
Capable of sensing when a user touches a display surface, touch panels may be classified into analog resistive, digital resistive, capacitive, saw, and infrared type touch panels.
Generally, touch panels are provided with upper and lower transparent substrates, each having upper and lower electrodes formed thereon, respectively. The upper and lower transparent substrates may be bonded to each other within a predetermined space.
If a surface of the upper transparent substrate is touched at a predetermined point using input means, e.g., a finger, a pen, etc., the upper electrode formed on the upper transparent substrate electrically connects to the lower electrode formed on the lower transparent substrate. A voltage, made variable by a resistance value or a capacitance value of the touched point, is then detected and outputted along with a location defined by coordinates of the touched point.
The touch panel described above is generally manufactured such that it is larger than the display device it is to be combined with. In integrating a display device such as an LCD with a touch panel, however, the size of the touch panel must be adjusted to correspond to the size of the LCD so that a dead space region of the touch panel is smaller than a liquid crystal margin of the LCD. Accordingly, integrating LCDs with touch panels generates a problem in manufacturing process steps.
A related art touch panel capable of being integrated with an LCD will now be explained with reference to the drawings described below.
FIG. 1 illustrates a plane view of a related art touch panel. FIG. 2 illustrates a sectional view of the related art touch panel taken along line I–II′ shown in FIG. 1. FIG. 3 illustrates a sectional view of the related art touch panel taken along line II–II′ shown in FIG. 1. FIG. 4 illustrates a sectional view of the related art touch panel taken along line III–III′ shown in FIG. 1. FIG. 5A illustrates a layout of an upper substrate of the related art touch panel shown in FIG. 1. FIG. 5B illustrates a layout of a lower substrate of the related art touch panel shown in FIG. 1.
In related art LCDs integrated with touch panels, touch panels are formed on display surfaces of display devices so that the touch panels may be used as a means for inputting signals on the display surface.
Referring to FIG. 1, a related art touch panel capable of being integrated with an LCD includes a viewing area V/A and a dead space region 20.
The viewing area is corresponds to the display surface of the display device and is surrounded by the dead space region. The upper and lower transparent substrates are bonded to each other via an insulating sealant provided in the dead space region 20.
Generally, the upper and lower transparent substrates comprise two opposing rectangular upper and lower substrates made out of a material having flexibility and transparency, e.g., polyethylene terephthalate (PET). The upper and lower transparent electrodes are formed on the opposing surfaces of the upper and lower PET substrates, respectively. The upper and lower PET substrates are spaced apart and bonded via an insulating sealant provided in the dead space region 20.
Accordingly, if a predetermined area of the upper substrate is touched with a pen or a finger, the transparent electrodes are also electrically connected to each other at the predetermined area so that a voltage, made variable by a resistance or a capacitance value of the touched point, is detected and outputted. In order to detect the voltage value outputted by the resistance value or the capacitance value at the predetermined area, a signal line connected to the upper transparent electrode in the dead spacer region 20 applies a voltage to the lower transparent electrode and receives the voltage, made variable by the touched area.
The related art touch panel will now be explained in greater detail with reference to the sectional views described below.
Referring to FIGS. 2 to FIG. 5B, upper lower and upper PET substrates 1 and 2 are formed in a size and a shape corresponding to the display surface of the display device. Upper and lower transparent electrodes 3 and 4 made out of a transparent electrically conductive material, e.g., ITO, etc., are formed in each opposing surface of the upper and lower substrates 1 and 2.
Metal electrodes, e.g., silver (Ag) paste, are formed in the dead space region 20 of the upper and lower substrates. As shown in FIGS. 2 and 5A, metal electrodes 5a and 5b are formed in a dead space region 20 and connected to the upper transparent electrode 3 at the right and left sides of the upper substrate 1. Metal electrode 5b is electrically connected to metal electrode 5c formed in a dead space region 20 on lower or upper side of the upper transparent substrate 1. Metal electrode 5c is electrically insulated from the upper transparent electrode 3 by an insulating layer 10a but is electrically connected to FPC 7 via a conductive sealant 8a, as is metal electrode 5a. 
As shown in FIGS. 2 and 5B, metal electrodes 6a and 6b formed in the dead space region 20 are connected to the lower transparent electrode 4 at lower and upper sides of the lower substrate 2. Metal electrodes 6a and 6b are also electrically connected metal electrode 6c formed in a dead space region 20 on the left side of the lower transparent substrate 2. Metal electrode 6c is electrically insulated from the lower transparent electrode 4 by an insulating layer 10b but is electrically connected to FPC 7 via a conductive sealant 8b.
FPC 7 acts as a signal line electrically connected to the metal electrodes 5(a and b) and 6(a and b) in the dead space region 20 by the metal electrodes 5(a and c) and 6c, respectively. Accordingly, two signal lines are printed on the upper and lower surfaces of the FPC 7 such that FPC 7 is electrically bonded to the metal electrodes 5a, 5c and 6c by the conductive sealants 8a or 8b. Accordingly, two signal lines printed on the upper surface of the FPC 7 are electrically bonded to the metal electrodes 5a and 5c, and two signal lines printed on the lower surface of the FPC 7 are electrically bonded to the metal electrode 6c. 
As mentioned above, FPC 7 is electrically bonded to the metal electrodes 5a, 5c and 6c via the conductive sealant 8a and 8b, and the upper and lower substrates are bonded to each other via an insulating sealant 9 provided in all portions of the dead space region 20 except at the portion of the dead region occupied by FPC 7.
A method for electrically bonding the FPC 7 to the metal electrodes 5a, 5c, and 6c will now be explained in detail.
First, conductive sealant 8a and 8b is deposited on the metal electrodes 5a, 5c, and 6c. Next, the insulating sealant 9 is deposited in the dead space region 20 except for the portion of the dead region occupied by FPC 7 . Subsequently, only the portion of the FPC 7 that is to be electrically connected to the metal electrodes 5a, 5c, and 6c, e.g., the portions of the FPC 7 on which the conductive sealant is formed, is heated at a temperature of approximately 100° C., and pressed to electrically connect the FPC 7 to the metal aforementioned metal electrodes. Through the electrical connection of the FPC 7 to the metal electrodes, the lower and upper transparent substrates are bonded to each other.
An operation of the touch panel will now be explained.
If the surface of the upper transparent substrate 1 is touched at the predetermined area with a pen or a finger, the upper and lower electrodes 3 and 4 become electrically connected to each other at the predetermined area.
Accordingly, a power supply voltage (Vcc) and a ground voltage (GND) are applied to the right and left sides of the upper transparent electrode 3 formed on the upper substrate 1 via the two signal lines formed on the upper surface of the FPC 7 and the metal electrode 5a, 5b, and 5c. A voltage, having a value made variable by the resistance value or the capacitance value specific to the touch point, is then outputted via the lower transparent electrode 4, the metal electrodes 6a, 6b, and 6c, and the two signal lines formed on the lower surface of the FPC 7, so that X-axis coordinates are detected.
Additionally, the power supply voltage Vcc and the ground voltage GND are also applied to the upper and lower sides of the lower transparent electrode 4 formed on the lower transparent substrate 2 via the two signal lines formed on the upper surface of the FPC 7 and the metal electrode 6a, 6b, and 6c. Then, the voltage value is then outputted at the touch point by the upper transparent electrode 3 and the metal electrodes 5a, 5b, and 5c of the upper substrate 1, so that the Y-axis coordinates are detected. Accordingly, the X-Y coordinates of the touch point may be detected.
However, the structure and method of operation of the aforementioned related art touch panel has the following problems.
First, when FPC 7 is electrically bonded to the various metal electrodes via the conductive sealant, the FPC is heated at a temperature of 100° C. At that temperature, the conductive sealant melts and deleteriously flows into the viewing area (V/A). Second, the upper and lower transparent electrodes formed on their respective substrates may electrically short at undesirable locations on the upper or lower transparent substrates due to the melting of the conductive sealant. Third, a contact failure occurs between the metal electrodes due to interference by the FPC.